Hi,

I've bought the clear cast epoxy resin for a "valley" table top I'm making. The total thickness will be approximately 28mm. The resin will only do 15mm in one pour. How do I go about doing the 2nd pour? Do I have to wait until it's full cured (several days??!) will the surface need sanding (keyed) before I pour the 2nd layer?


Also, I will need to sand the resin once fully cured, because the want the wood either side of the resin to be visible (not covered in resin) so will I need to go through all the grits 120-1500 wet dry and then use a cutting compound to polish it?


Any help will be greatly appreciated!

Thank you.

Hi,

There are two ways of doing it.  First is to wait until the resin is part cured at the firm but tacky B stage - which needs careful monitoring to get the timing right.  The second is to allow the resin to fully cure before the second application. These are two options for ensuring a good bond between separately poured layers.

OPTION 1: B-Stage
In most cases, a second layer can be poured onto a previous layer if the original layer is at its ‘B-stage’. This means that the resin has gone firm but still has a still tack left in the surface. At this stage, it is possible to pour the new layer over the top of the original layer without the need for any surface preparation because during this B-stage, the two layers will still form a chemical bond.

If the original layer has cured past its B-stage, i.e. once there is no longer any tack left in the surface of the original pour, it becomes necessary to allow the first pour to cure fully and then ‘key’ the surface using a coarse abrasive paper; see OPTION 2.

OPTION 2: Cure then Key
If the original layer has cured past its B-stage (see OPTION 2) then a second pour of resin will no longer be able to chemically bond to the first layer. Instead, we must ensure a good mechanical bond between the two layers. In order to achieve this it is necessary to ‘key’ the surface of the original layer using a coarse abrasive paper such as P120 wet-and-dry paper.

Before keying the surface, it’s important to ensure that the first layer of resin is fully cured (not tacky on the surface). Use a sheet of coarse abrasive paper (such as P120) to ‘key’ or scratch the entire surface. Don’t worry that the surface then looks scratched and light in colour - this will disappear as soon as the next layer of resin is poured.


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Thank you for your reply, it was very helpful!

I did the first seal coat which went very well, I got a few bubbles which I managed to get rid of using my hot air gun. I let tha set (about 30hrs) it was rock hard and not tacky. I sanded the surface like you said, making sure it was all sanded and then cleaned the surface. I then did the first main pour, but this time I had thousands of tiny bubbles appear, non of which I could pop with the air gun. I mixed the resin for about 4 mins until totally smooth, any idea on what could have gone wrong?

I'll try and post a photo, but it's very difficult to see then.

For some reason it won't upload my photos even though I've made them really small.

I used the 3 pot method to make sure only one pot was used to mix the resin.

Its hard to tell from the picture but are the bubbles in the surface coat or the sealing coat?  It could be the sealing coat had some voids in that opened up with sanding and now show up. It's not something we have seen like that before.  How humid is the environment?  Excessive moisture can cause a reaction similar.

Recovery would involve sanding it right back and starting afresh..



Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

The bubble are in the main coat, not the sealant coat. The seal coat was perfect.

I don't know if there was too much moisture in the air, I have now way of testing that.